By UN projections, the world population will reach over 10 billion in 2050 before it stabilizes.
That is double the present 5.5 billion.
However, depending on whether birthrates continue to fall, the 2050 population could end up somewhere between 7.8 and 12.5 billion.
Economics, religion, and women's education are major factors that influence population growth or decline.
Wherever governments have encouraged family planning, birth rates have dropped.
Countries which have seen birth rates decline include Egypt, China, India, Tunisia, and Brazil.
Iran's clerics, who initially encouraged large families, now encourage family planning, which has dropped their growth rate from 3.9% to 2.3%.
Birth rates in Latin American countries have fallen dramatically, with growth rates under 2%.
However, growth rates in Mexico and the Philippines remain high at 2.4% Africa's growth rate of 2.9% is the highest in the world.
Sub-Saharan Africa has fertility rates over 6 per woman.
The World Bank projects a doubling of the population to one billion in the next 30 years.
Family planning is encouraged only in Zimbabwe and Botswana.
In the coming years, industrialized countries can expect slow growth at a rate of 1% in North America,.5% in the former Soviet Union, and .3% in Europe.
Eastern Germany's fertility rate has plummeted to .8, mainly due to the change in economics and the new-found freedom to travel.
Singapore's "two is enough" policy was too successful, drastically shrinking its population.
It now offers tax incentives to have a third child .
